External-rotor motor having a stationary bearing shaft

ABSTRACT

An improved drum motor, preferably electronically commutated, features a unitary stationary central shaft ( 18 ) supporting a stationary inner stator ( 52 ), and an external rotor ( 49 ), including permanent magnets ( 54 ), secured to an inner surface of a generally cylindrical rotatable casing part ( 18 ). This permits variable speed operation while avoiding any need for an internal gear linkage. Safety is improved by making sealing plates ( 76, 78 ) at respective axial ends of the casing ( 14 ) stationary, and providing an annular peripheral seal ( 90 ) around each sealing plate. Respective rolling bearings ( 24, 44 ) near each end of the casing ( 14 ) facilitate rotation of the external rotor ( 49 ) relative to the stator ( 52 ), and a clamping arrangement ( 30 ) minimizes noise from the bearings.

This application is a divisional of application Ser. No. 10/733,117,NICKEL-JETTER et al., filed 11 Dec. 2003, now U.S. Pat. No. 7,049,718now allowed.

FIELD OF THE INVENTION

The present invention relates generally to an external rotor motorhaving a stationary bearing shaft, and more particularly to a drummotor.

BACKGROUND

German Utility Model DE 296 23 889 U1, JOERISSEN, discloses a so-calleddrum motor that is used in a variety of industries, for example to driveconveyor belts. In that document, the drum tube is secured at both endsto a respective cover, that therefore rotates together with the drumtube, and is driven via a gear linkage by a motor in the interior of thedrum tube. To permit better cleaning, a cap made of stainless steel isadhesively bonded onto each cover.

SUMMARY OF THE INVENTION

It is an object of the invention to provide an improved motor of thegeneral type just described.

According to the invention, this object is achieved by replacing thegear drive with a stationary central stator which cooperates with apermanent magnet external rotor on an inner surface of a casing partrotatable relative to the stator.

It is thereby possible to drive the casing part directly by means of theexternal rotor motor that is used, thus resulting in a simple design andeliminating the need to use a gear linkage. Electronic commutationproves very advantageous in this context, because it permits not onlydrive operation at high rotation speeds but also drive operation at verylow rotation speeds—thus eliminating the need for an adjustable gearlinkage—and because, in such a motor, the rotation speed is easilymodifiable, e.g. by modifying the operating voltage.

A further advantageous feature of the invention is to make the axial endcovers of the drum tube stationary, and to provide an annular seal withrespect to the adjacent drum tube ends. A closure member of this kind isjoined to the stationary support part, i.e. does not rotate, thusreducing the risk of injury at this point and also simplifying andfacilitating cleaning, e.g. in the food industry or the pharmaceuticalindustry.

BRIEF FIGURE DESCRIPTION

Further details and advantageous features of the invention are evidentfrom the exemplary embodiment described below, which is in no way to beunderstood as a limitation of the invention.

FIG. 1 is a longitudinal section through a preferred embodiment of anelectronically commutated external rotor motor according to theinvention; and

FIG. 2 is an enlargement of detail A of FIG. 1, showing the relativepositions of stationary stator and external rotor.

DETAILED DESCRIPTION

In the description that follows, terms such as “left” and “right” referto the respective figure of the drawings.

FIG. 1 shows a so-called “drum motor” 10 that is driven directly by anelectronically commutated external rotor motor 12 and preferably isadapted to drive conveyor belts. It has an external tubular casing part14 made of ferromagnetic material, preferably steel, that can be ofslightly convex configuration on its outer side 16.

External rotor motor 10 has a stationary support part 18 that, becauseof its appearance, is often referred to informally as a “shaft.” Thisshaft 18 is stationary during operation, i.e. does not rotate.

This stationary shaft 18 has a cylindrical segment 20, of greaterdiameter, on which is mounted inner race 22 of a ball bearing 24, whoseouter race 26 is arranged displaceably inside a cylindrical innersurface 28 of casing part 14 and is acted upon, toward the right, by acompression spring 30 whose left end is braced against a prong ring 32or other abutment. A prong ring has, on its external periphery, one ormore prongs which, upon assembly, dig into the cylindrical inner surface28 of casing part 14, the result being that prong ring 32 constitutes anabutment for compression spring 30, so that the latter can clamp ballbearing 24, which contributes to noise reduction.

Shaft 18 furthermore has a cylindrical segment 36 of smaller diameter,on which is mounted inner race 38 of a ball bearing 40, whose outer race42 is arranged on a cylindrical portion 44 of casing part 14 and issecured there on the left by a shoulder 46 and on the right by a snapring 48. The two ball bearings 24, 40 therefore have different sizes,and they support casing part 14 rotatably on shaft 18.

Mounted in the cylindrical inner recess 28 of casing part 14 arepermanent magnets 50 of external rotor motor 12, which define anexternal rotor 49. This is then magnet arrangement 50 of the motor part,which extends to the left from a shoulder 51 and coacts with an internalstator 52 whose lamination stack 54 is pressed onto shaft 18, whichpreferably is likewise made of ferromagnetic material and thus formspart of the magnetic circuit of internal stator 52. Shaft 18 is equippedwith a shoulder 56 that defines the location of the lamination stack.

Adjoining permanent-magnet arrangement 50 to the left is a nonmagneticspacer ring 58, made e.g. of brass, and this is followed to the left bya magnet ring 60 that serves to control one or more galvanomagneticsensors 62, e.g. to control Hall generators (not depicted). The functionof sensors 62 is to sense the rotational position of casing part 14relative to stationary axis 18, which must occur very precisely,especially when motor 12 is running slowly and a rotation speed controlsystem is being used.

Magnets 50, 60 are preferably magnetized in the radial direction. Magnetarrangement 50 can be implemented with, for example, four poles, andmagnet ring 60 preferably has a greater number of poles, so that therotational position can be sensed as accurately as possible.

Sensor 62 is mounted on a circuit board 66, which in turn is mounted onshaft 18 and carries electronic components of the electronicallycommutated external rotor motor 12, and extends approximatelyperpendicular to rotation axis 67 of casing part 14. For passage of aconnection to circuit board 66, shaft 18 has an axial bore 68 and aradial bore 70 intersecting it. The winding of motor 12 is indicated at72.

Two sealing plates 76, 78 are provided to seal the interior of drummotor 10. These are of identical configuration, so a description ofright sealing plate 78 will suffice. The latter has, on its radiallyinner side, a portion 80 that can deflect radially outward and isequipped with an inwardly projecting catch ridge 82 that, in theassembled state, engages into an annular groove 84 of shaft 18 that isapproximately complementary to it.

Shaft 18 is formed, in a region to the left of sealing plate 76, with afrusto-conical segment 86 to facilitate assembly of sealing plate 76,and with a frusto-conical segment 88 to facilitate assembly of sealingplate 78. This makes it easier to splay, and slide on, sealing plates76, 78 during final assembly. It is very advantageous that sealingplates 76, 78 do not rotate; this decreases the risk of injury to theuser, and simplifies cleaning of drum motor 10. Sealing plates 76, 78can be made of metal or a suitable plastic.

On its outer side, sealing plate 78 is equipped with two sealingelements 90, e.g. two sealing lips, a radial packing ring, or the like.The inner surface of casing part 14, located opposite sealing elements90, is ground and polished. To facilitate assembly, hollowfrusto-conical segments 92 are provided on the inner side of casing part14, adjacent the sealing plates.

With the invention, in contrast to drum motors having an internal gearlinkage, shaft 18 can be continuous, thus imparting particularly highstability to drum motor 10. Electronically commutated motor 12 does nothave a rotatable shaft. The continuous stationary shaft 18 means thattwo rolling bearings 24, 40 are sufficient. Since casing part 14 isintegral with external rotor motor 12, rather than a separate element,the weight of drum motor 10 is correspondingly reduced.

Assembly

Motor magnets 50, spacer 58, and magnet ring 60 are adhesively bondedinto casing part 14, optionally with spot-grinding, and then magnetizedin a suitable apparatus. Rolling bearing 40 is also installed in recess44 and secured with snap ring 48.

The stator lamination stack is pressed onto shaft 18, and circuit board66 is mounted on shaft 18. Ball bearing 24 is then pressed onto shaft 18at the desired location.

After these preparatory actions, shaft 18, along with the partsinstalled on it, is inserted with its insertion end (i.e. right end 94in this case) into the prepared casing part 14 from the left. Insertionis facilitated by the fact that outer race 26 of left ball bearing 24 isaxially displaceable in recess 28, to allow it to be axially clamped byspring 30.

In the process, segment 36 of shaft 18 is pressed into inner race 38 ofrolling bearing 40, and sensor 62 is slid into the interior of controlmagnet 60. An important advantage of the invention is that the controlelectronics (on circuit board 66) are integrated into motor 10.

External connection of motor 10 is accomplished through transverse bore70 and longitudinal bore 68. To simplify assembly, an electrical plugconnector (not depicted) can be provided at the transition fromtransverse bore 70 to longitudinal bore 68.

Depending on the application, one or more Hall generators or a resolver,a GMR (Giant Magneto Resistor) sensor, an MR sensor, etc. can be used assensor 62. Sensing of the rotor position using the so-called“sensorless” principle is also not excluded in the context of theinvention.

Spring 30 is then introduced and is placed under load and secured byprong ring 32 or another securing element. Lastly, sealing plates 76, 78are installed. Assembly is thus very simple and time-saving. Shaft 18can optionally be put together from several parts, but a one-piececonstruction is preferred. The use of a large-diameter shaft, andbearings with small radial dimensions, yields the advantage that verygood heat transfer out from the stator lamination stack 52 via shaft 18is possible.

An air gap 80, shown in the enlargement in FIG. 2, is located betweenrotor magnets 50 and lamination stack 54.

Many variants and modifications are of course possible within the scopeof the present invention. Although motor 12 is shown as an externalrotor motor having a permanent magnet rotor 50, in other embodiments therotor can nevertheless also be implemented as a short-circuit rotor(having a short-circuit winding), a synchronous motor, a reluctancemotor (having a magnetically soft rotor), etc. Since a collectorlessmotor allows very different rotation speeds to be set without greatdifficulty, the structure shown is particularly preferred for lowrotation speed applications.

Rotor magnets 50 may have a trapezoidal or sinusoidal magnetizationdepending on the motor principle used, a trapezoidal magnetization beingpreferred for rotor magnets 50, and a sinusoidal magnetization beingpreferred for sensor magnets 60.

1. An external rotor motor (12), comprising an internal stator (52); astationary support part (18) supporting the stator; and an externalrotor (49), cooperating with the internal stator (52), and mounted onbearings for rotation with respect to the stator, said rotor having acasing part (14) on whose inner side (28) is arranged a permanent-magnetarrangement (50) that coacts with the internal stator (52), a first sideof said casing part (14) being supported by means of a first rollingbearing (24) on said stationary support part (18), said first bearinghaving an outer race (26) slidably arranged adjacent an inner surface(28) of said casing part (14) and having an inner race (38) fixed tosaid stationary support part (18); a second side of said casing part(14) being supported by means of a second rolling bearing (40) on saidstationary support part (18), said second bearing having an outer race(42) nonslidably secured adjacent the inner surface (28) of said casingpart (14) and having an inner race (38) fixed to said stationary supportpart (18); and wherein the outside diameter of the outer race (26) ofsaid first rolling bearing is dimensioned such that the stationarysupport part (18), along with said internal stator (52) and said firstrolling bearing (24) mounted thereon, fits into said casing part (14)for purposes of assembling said motor.
 2. The motor of claim 1, furthercomprising a shoulder (46), formed on said inner surface of said casingpart (14), and a snap ring (48), which together secure in place saidouter race (42) of said second rolling bearing (40).
 3. The motor ofclaim 2, further comprising at least one spring which engages againstsaid slidable outer race (26) of said first rolling bearing (24).
 4. Themotor of claim 3, further comprising a prong ring (32) having prongswhich engage into the inner surface of said casing part (14).
 5. Themotor of claim 1, further comprising at least one spring which engagesagainst said slidable outer race (26) of said first rolling bearing(24).
 6. The motor of claim 5, further comprising a prong ring (32)having prongs which engage into the inner surface of said casing part(14).
 7. The motor of claim 1, wherein said first and second rollingbearings differ in size.
 8. The motor of claim 1, wherein a sensorarrangement (62, 66), for sensing the rotational position of theexternal rotor (49) relative to the internal stator (52), is arrangedbetween the first rolling bearing (24) and the internal stator (52)mounted on the support part (18).
 9. The motor according to claim 8,wherein the sensor arrangement (62, 66) has, associated with it, acontrol magnet (60) mounted on the inner side (28) of the casing part(14), the number of whose poles is greater than the number of magneticpoles (50), coacting with the internal stator (52) and secured to thecasing part (14), of the external rotor (49).
 10. The motor according toclaim 9, wherein a nonmagnetic spacer ring (58) is arranged between themagnet poles (58) of the external rotor (49) and the control magnet(60).
 11. The motor according to claim 9, wherein the support part (18)has at least one portion (86, 88) of frusto-conical shape on which ismounted at least one closure member (76, 78) which, along with a sealingelement (90), engages against the inner surface (28) of said casing part(14).
 12. The motor according to claim 11, wherein the closure member(76, 78) has, on its inner periphery, a protrusion (82) that engagesinto a corresponding recess (84) of the support part (18).
 13. The motoraccording to claim 11, wherein one closure member (76,78) has, in itsradially inner region, a resilient portion (80), in order to facilitateassembly onto said stationary support part (18).
 14. The motor accordingto claim 9, wherein said stationary support part (18) has at least oneportion (86, 88) of frusto-conical shape, in order to facilitatemounting of the closure element onto the support part (18).
 15. Themotor according to claim 9, wherein an inner surface (28) of saidsupport part (18) is formed with a frusto-conical portion (92) in orderto facilitate assembly of said closure member (76, 78) into said casingpart (14).
 16. The motor according to claim 9, wherein in order toconstitute a magnetic return path for a permanent magnet (50, 60) of therotor, the casing part (14) is made at least locally of a ferromagneticmaterial.
 17. The motor of claim 1, further comprising means forelectronically commutating said motor.